1. Field of the Invention
This invention relates generally to flow control valves in which the flow through the valve is generally proportional to the signal applied to the valve actuator.
2. Description of the Background Art
In the past a wide variety of valves have been developed in which the flow through the valve is controlled proportionally to the current through an actuator such as an electromagnetic type actuator. For example, the following U.S. patents disclose various means for controlling the flow of a fluid in proportion to the applied current or voltage; U.S. Pat. Nos. 3,054,426, 3,172,021, 3,423,020, 3,435,395, 3,571,769, 4,132,384, 4,150,351, and 4,170,339.
In. U.S. Pat. No. 3,054,426 to Fritz et al, a variable flow valve and a separate shut-off valve are disclosed for control of a gas furnace. Fattor in U.S. Pat. No. 3,244,397 teaches the use of a tapered valve that achieves firm shut off by an extra actuator that forces the valve firmly into its seat.
In addition a number of prior fluid flow control valves have used electromagnetically operated flaps to control the fluid flow. For example, the following U.S. patents disclose valves of this general type: U.S. Pat. Nos. 3,176,516, 3,645,495, 3,968,898, 4,089,348, and 4,114,852.
While prior structures have succeeded to various degrees in providing a low cost, dependable and effective electromagnetically operated proportional flow control valve, there is a continuing need for new and improved devices of this type.